CORRELATION OF LEAF DAMAGE WITH UPTAKE AND TRANSLOCATION OF GLYPHOSATE IN VELVETLEAF (ABUTILON-THEOPHRASTI)

Uptake and translocation of glyphosate in three commercial formulation s were examined in velvetleaf, a dicotyledonous weed that is commonly treated with glyphosate. The formulations included Roundup(R) (MON 350 85), Roundup Ultra, and Touchdown(R) as sold in Canada. A minimal amou nt of C-14-glyphosate was spiked into a lethal rate of each formulatio n, and the short-term (3 to 72 h) uptake into the treated leaf and sub sequent translocation into the plant were measured. Time-course studie s showed very rapid uptake and translocation of glyphosate in the Ultr a formulation. In comparison, the uptake and translocation of glyphosa te in Touchdown was much slower but continued throughout the 72-h peri od. Glyphosate in the Roundup formulation showed intermediate uptake a nd translocation. Tissue necrosis at the application sites of Ultra an d Roundup was visible within 24 h after treatment. Examinations using stereo and fluorescence microscopy revealed extensive cell death and t issue disruption. Tissue necrosis from Ultra and Roundup was also obse rved in blank formulations containing no glyphosate and therefore was likely caused by the surfactants. In contrast, the application sites o f Touchdown produced little to no leaf damage. Our results demonstrate d a direct correlation between tissue necrosis and rapid rates of glyp hosate uptake and translocation.